1. Field of the Invention
The present invention relates to a compressor for use in a household refrigerator or refrigerating air conditioner.
2. Description of the Related Art
This type of compressor has a cylinder, a cylinder bore formed in the cylinder, and a piston that reciprocates inside the cylinder bore to compress a gas (refrigerant or the like). For example, in Unexamined Japanese Patent Publication No. S54-77315 and Unexamined Japanese Patent Publication No. 2002-89450, there is disclosed a constitution in which in order to reduce a sliding loss between the piston and the cylinder bore, the cylinder bore is partially tapered.
Moreover, on an opening surface side of the cylinder bore in a piston compression direction, suction and exhaust are performed by a discharge valve, a suction valve, a valve plate, a cylinder head and gaskets. A series of components such as the discharge valve and the like are mounted on, and fixed to the cylinder by bolts.
Moreover, in Unexamined Japanese Patent Publication No. S56-12079 and Unexamined Japanese Patent Publication No. S63-230975, there is disclosed a constitution in which distortion of the cylinder bore is avoided in view of a fact that in the cylinder bore, the distortion is caused by tightening of the bolt.
FIG. 8 is a vertical cross-sectional view of a conventional compressor, FIG. 9 is a plan view of a substantial portion in which a part of the same compressor is cut out, and FIG. 10 is a plan view of a substantial portion in which a part of another conventional compressor disclosed in Unexamined Japanese Patent Publication No. S56-12079 is cut out.
In FIGS. 8 and 9, compressor 1 centers on cylinder block 4, and electric element 5 is arranged in a lower portion of hermetic container 2, and compression element 6 is arranged in an upper portion thereof. Compression element 6 and electric element 5 are each a part of cylinder block 4. Compression element 6 and electric element 5 are elastically supported by hermetic container 2 through suspension spring 3.
Compression element 6 is made up of piston 7, cylinder 8, suction gasket 9, valve plate 10, discharge valve gasket 11, a discharge valve and a suction valve not shown, valve seat cover 12 and the like. These are fastened by bolt 13 screwed into screw holes 8a provided in cylinder 8 from a valve seat cover 12 side.
Screw holes 8a are opened in the vicinity of cylinder bore 8b in which piston 7 slides. Bolts 13 are screwed into screw holes 8a to fasten valve seat cover 12, discharge gasket 11, valve plate 10, and suction gasket 9 to cylinder 8.
In Unexamined Japanese Patent Publication No. S56-12079 shown in FIG. 10, deformation of an inner diameter of cylinder bore 8b when bolts 13 are fastened is pointed out, and a constitution for a solution is described.
In FIG. 10, bolts 22 are caused to penetrate cylinder 21, suction gasket 9, valve plate 10, discharge gasket 11, valve seat cover 12 and the like in a combined state, and are then fastened with nuts 23 in screw hole portions 22c projected from valve seat cover 12. This allows bolt head portions 22b to be contained in cylinder counterbore portions 21b. As a result, bolts 22 do not fasten vicinities of cylinder bores 21c. Bolts 22 are fastened with nuts 23, thereby making distortion of cylinder bores 21c smaller.
Next, FIG. 11 is a cross-sectional view of a substantial portion of still another conventional compressor disclosed in Unexamined Japanese Patent Publication No. S54-77315.
In FIG. 11, a basic constitution of the compressor is the same as that of FIG. 8. Piston 52 reciprocates inside cylinder bore 51 to thereby compress a gas such as a refrigerant suctioned from suction hole 54 and exhaust the same from discharge hole 55. In FIG. 11, a discharge valve, a suction valve and the like are not shown. A space surrounded by piston 52 and cylinder bore 51 is sealed by sealing 56 of piston 52 and piston 52. Cylinder bore 51 is provided with cylindrical portion 57, in which a side where piston 52 moves for compression is flat, and tapered portion 58 on an opposite side of the side for compression (anti-compression side). This reduces sliding between piston 52 and cylinder bore 51, thereby decreasing the sliding loss.
However, in the above-described conventional constitution, in the case where tapered portion 58 is provided in cylinder bore 51 in order to decrease the sliding loss, there are problems below.
First, using the conventional examples in FIGS. 9 and 10, the bore distortion will be described. In the constitution shown in FIG. 9, the distortion due to the fastening of bolts 13 occurs in cylinder bore 8b. 
Moreover, as for the constitution shown in FIG. 10, for the fastening of valve seat cover 12, valve plate 10 and the like to cylinder 21 using bolts 22 and nuts 23, portions corresponding to bolts 22 in cylinder 21 are largely removed for insertion of bolts 22. Thus, in the cylinder 21 portion, a portion where a thickness of a wall of cylinder bore 21c is thinner is formed, and in the portion of the thinner wall, the distortion due to the fastening of bolts 22 remains. Furthermore, back in a machining process, when cylinder bore 21c is machined, distortion due to stress and heat generated by a machining tool lowers machining accuracy of cylinder bore 21c, because the wall thickness is partially thinner. Moreover, because of the distortion due to the stress and the heat generated by the machining tool, it is difficult to make a clearance (gap) between cylinder bore 21c and piston 7 smaller.
Moreover, as described before, since the wall thickness of cylinder bore 21c is partially thinner, the distortion also occurs when bolts 22 are fastened, which makes it difficult to keep cylinder bore 21c in a highly accurate cylindrical shape.
Next, using the conventional example in FIG. 11, a reduction in sliding loss due to taper formation of cylinder bore 51 will be described.
In FIG. 11, cylindrical portion 57 is formed on the compression side of cylinder bore 51, and tapered portion 58 is formed on the anti-compression side to thereby reduce the sliding loss. In this case, however, unless a length of cylindrical portion 57 is made shorter, an expected effect of the sliding loss reduction cannot be obtained.
On the other hand, to make cylindrical portion 57 shorter is to make shorter a length of a portion where the clearance between piston 52 and cylindrical bore 51 is small, that is, a length of a sealed portion, which easily causes leakage of the gas such as the refrigerant. Moreover, retention in the gap of a lubricant (not shown) sealing the clearance portion, that is, the gap between cylinder bore 51 and piston 52 is deteriorated. As a result, an increase in compression loss due to the leakage of the gas (i.e., a decrease in compression efficiency), and a decrease in reliability due to shortage of the lubricant are brought about.
Here, in order to eliminate the reduction in sliding loss and the leakage of the gas, to make smaller the clearance between cylindrical portion 57 and piston 52 can be easily considered. However, as described in FIGS. 8, 9, and 10, in order to make the gap smaller, the distortion in machining needs to be reduced, and an influence by the distortion when the bolts 13 and 22 are tightened needs to be eliminated. Since the sliding portion (which denotes cylindrical portion 57) is short, when the distortion occurs, a contact pressure between piston 52 and cylinder bore 51 becomes higher, which brings about a decrease in reliability.
Accordingly, in the related art, there has been a problem that it is difficult to reduce the leakage of the gas from the gap between cylindrical portion 57 and piston 52, thereby maintaining the compression efficiency, and further assure the reliability while decreasing the sliding loss and enhancing the machine efficiency.